BS ISO 7238-2004 en_9689 Butter - Determination of pH of the serum - Potentiometric method《奶油.乳清pH值的测定.电位滴定法》.pdf

1、BRITISH STANDARD BS ISO 7238:2004 Butter Determination of pH of the serum Potentiometric method ICS 67.100.20 BS ISO 7238:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 8 December 2004 BSI 8 December 2004 ISBN 0 580 44987 4 National for

2、eword This British Standard reproduces verbatim ISO 7238:2004 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee AW/5, Milk and milk products, which has the responsibility to: A list of organizations represented on this committ

3、ee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facilit

4、y of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.

5、aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages

6、This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 5 and a back page. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Ref

7、erence numbers ISO 7238:2004(E) IDF 104:2004(E) OSI DI dnaF 4002INTERNATIONAL STANDARD ISO 7238 IDF 104 Second edition 2004-12-01 Butter Determination of pH of the serum Potentiometric method Beurre Dtermination du pH de la phase aqueuse Mthode potentiomtrique BSISO7238:2004IS:8327 O4002(E) ID:401 F

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13、opyrightisoo.rg -Emailni off-lidif.org We bwww.is.o gro We bwww.fil-idf.o gr Plbuisdehi n Switlrez dnaii ISO dnaID 4002 FA ll rihgtsser edevrBSISO7238:2004IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr iiiContents Foreword iv 1 Scope 1 2 Normative references . 1 3 Terms and

14、definitions. 1 4 Principle . 1 5 Reagents 1 6 Apparatus. 2 7 Sampling 2 8 Procedure. 3 8.1 Test portion . 3 8.2 Separation of the serum. 3 8.3 Calibration of the pH-meter 3 8.4 Determination 3 8.5 Cleaning the electrodes 3 9 Expression of results 3 10 Precision 4 10.1 Repeatability 4 10.2 Reproducib

15、ility 4 11 Test report 4 Bibliography . 5 BSISO7238:2004IS:8327 O4002(E) ID:401 F002(4)E iv I SO dna ID 4002 F All irhgts seredevrForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing Intern

16、ational Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with

17、 ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical

18、 committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to

19、the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 7238 IDF 104 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, a

20、nd the International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. This edition of ISO 7238 IDF 104 cancels and replaces ISO 7238:1983, of which it constitutes a minor revision. Only editorial chan

21、ges have been made. BSISO7238:2004IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr vForeword IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National Committee in every member country. Every National Committee has the right to be r

22、epresented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO and AOAC International in the development of standard methods of analysis and sampling for milk and milk products. Draft International Standards adopted by the Action Teams and Standing Committees ar

23、e circulated to the National Committees for voting. Publication as an International Standard requires approval by at least 50 % of the National Committees casting a vote. ISO 7238 IDF 104 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the

24、 International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. All work was carried out by the Joint ISO/IDF/AOAC Group of Experts, pH of butter (E36), under the aegis of its project leader, Mr L.J.

25、Pootvliet (NL). This edition of ISO 7238 IDF 104 cancels and replaces IDF 104A:1984. Only editorial changes have been made. BSISO7238:2004blank 4002:8327OSISBNITERNATNOIAL STANDARD IS:8327 O4002(E) ID:401 F002(4)EI SO dna ID 4002 F All irhgts seredevr 1Butter Determination of pH of the serum Potenti

26、ometric method 1 Scope This International Standard specifies a potentiometric method for the determination of the pH of the serum from all types of butter. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the

27、 edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696:1987, Water for analytical laboratory use Specification and test methods 3 Terms and definitions For the purposes of this document, the following terms and defin

28、itions apply. 3.1 pH of butter serum potential difference at the measuring temperature between two electrodes immersed in butter serum, determined by the procedure specified in this International Standard NOTE It is expressed in pH units. 4 Principle The potential difference is measured between a gl

29、ass electrode and a reference electrode in the serum separated from melted butter. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and recently distilled water that has been protected from absorption of carbon dioxide and that complies with the requirements f

30、or grade 1 water specified in ISO 3696:1987. BSISO7238:2004IS:8327 O4002(E) ID:401 F002(4)E 2 I SO dna ID 4002 F All irhgts seredevr5.1 Buffer solutions, for calibration of the pH-meter. Two standard buffer solutions, having pH values known to the second decimal place at the measuring temperature, a

31、nd which will bracket the pH value of the serum obtained from the test portion, shall be used, for example a buffer solution of pH approximately 4 and another of pH approximately 7. EXAMPLES The following buffer solutions may be used: a) Buffer solution of pH 4,00 at 20 C and 4,01 at 25 C Dissolve,

32、in water, 10,12 g of potassium hydrogen phthalate (KHC 8 H 4 O 4 ), which has been previously dried to constant mass at 120 C. Make up to 1 000 ml with water at the measuring temperature and mix well. Preserve the solution by adding approximately 2 ml of chloroform or carbon tetrachloride. b) Buffer

33、 solution of pH 6,88 at 20 C and 6,86 at 25 C Dissolve, in water, 3,388 g of potassium dihydrogen orthophosphate (KH 2 PO 4 ) and 3,533 g of disodium hydrogen orthophosphate (Na 2 HPO 4 ), both compounds having been previously dried to constant mass at 120 C. Make up to 1 000 ml with water at the me

34、asuring temperature and mix well. Preserve the solution by adding approximately 2 ml of chloroform or carbon tetrachloride. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 pH-meter, of minimum sensitivity 0,01 pH unit, with a glass electrode and a suitable reference ele

35、ctrode, and with temperature compensation. The glass and reference electrodes may be assembled into a system of combined electrodes. 6.2 Centrifuge (if required), of the vertical-loading type 1) , capable of attaining a relative radial acceleration of approximately 375 g. 6.3 Centrifuge tubes (if re

36、quired), of capacity approximately 50 ml, with suitable stoppers. 6.4 Test tubes, of capacity approximately 12 ml, internal diameter 16 mm to 20 mm. 6.5 Water bath (if required), capable of being maintained at 65 C. 6.6 Ice-water bath (if required). 6.7 Calibrated thermometer, accurate to 1 C. 7 Sam

37、pling A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 7071 . 1) For details of a suitabl

38、e centrifuge, reference should be made to ISO 2446:1976, 6.6. BSISO7238:2004IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr 38 Procedure 8.1 Test portion Take approximately 50 g of the sample. 8.2 Separation of the serum Separate the serum from the butter by an appropriate me

39、thod (see the Note). Transfer the serum (including the protein) to a test tube (6.4), and bring it to the measuring temperature. NOTE There are many methods for the separation of the serum from the butter, one of which is as follows. Transfer the test portion to a centrifuge tube (6.3), and place th

40、e centrifuge tube in the water bath (6.5). Two layers will be formed by the melting butter. As soon as the butter has melted (after 3 min to 5 min), close the centrifuge tube with the stopper, place it, with the stoppered end downwards, in the tube holder and centrifuge for 5 min at a relative radia

41、l acceleration of approximately 375 g. Immediately immerse the centrifuge tube, with the stoppered end downwards, in the ice-water bath (6.6) and leave until the fat has completely congealed. 8.3 Calibration of the pH-meter Adjust the temperature of the buffer solutions (5.1) to the measuring temper

42、ature and calibrate the pH-meter in accordance with the manufacturers instructions. If a series of samples is being tested, check the calibration of the pH-meter with one or both buffer solutions at least every 30 min. 8.4 Determination Introduce the electrodes into the serum at the measuring temper

43、ature. Carry out the determination using the procedure appropriate to the pH-meter used. When the reading becomes constant, read the pH directly from the scale of the instrument, to the nearest 0,01 pH unit. Introduce the thermometer (6.7) into the serum and read the measuring temperature. 8.5 Clean

44、ing the electrodes Clean the electrodes by rinsing consecutively with acetone at room temperature and water at 30 C to 35 C. Dab them dry with a clean paper tissue. 9 Expression of results Record the measured pH to the nearest 0,01 pH unit, together with the measuring temperature. BSISO7238:2004IS:8

45、327 O4002(E) ID:401 F002(4)E 4 I SO dna ID 4002 F All irhgts seredevr10 Precision 10.1 Repeatability The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment wit

46、hin a short interval of time, will in not more than 5 % of cases be greater than 0,03 pH unit. 10.2 Reproducibility The absolute difference between two single test results, obtained using the same method on identical test material in different laboratories with different operators using different eq

47、uipment, will in not more than 5 % of cases be greater than 0,10 pH unit. 11 Test report The test report shall specify: a) all information necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this International Sta

48、ndard; d) all operating details not specified in this International Standard, or regarded as optional, together with details of any incidents which may have influenced the test results; e) the test results obtained, or, if the repeatability has been checked, the final quoted result obtained. BSISO72

49、38:2004IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr 5Bibliography 1 ISO 707, Milk and milk products Guidance on sampling 2)2 ISO 2446:1976, Milk Determination of fat content (Routine method) 2) Equivalent to IDF 50. BSISO7238:2004BS ISO 7238:2004 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British